The present application claims priority to French Application No. 01/01028 filed Jan. 25, 2001, the entire text of which is specifically incorporated by reference herein without disclaimer.
1. Field of the Invention
The present invention relates in general terms to a method for incorporating additives, and in particular pigments and/or dyes, into thin films, and to the use of this method for incorporating additives into ophthalmic lenses, in particular for colouring these ophthalmic lenses.
The invention also covers the ophthalmic lenses thus obtained.
2. Description of Related Art
Ophthalmic lenses made from organic materials are most often coloured in the bulk of the material by dipping in aqueous coloration baths, heated to temperatures of the order of 90xc2x0 C. and in which the pigments have been dispersed. The pigments thus diffuse under the surface of the substrate and the colour density is obtained with a quantity of the pigment having diffused into the body of the substrate.
These coloration operations are delicate since they depend on the affinity between the pigment and the material constituting the substrate.
Since ophthalmic lenses are composed of several different materials, each of a different nature, it is necessary to adapt the treatment for each of these, which is costly in terms of time and personnel assigned to the task. This is rendered even more difficult when it is desired to obtain colours requiring the penetration of several pigments and the treatment may need to be repeated several times after visual checking by operators.
Ophthalmic lenses are conventionally coated with an anti-scratch coating. It is known that various additives (pigments, UV absorbers) may be incorporated into the anti-scratch coating compositions before their application and hardening on one face of the ophthalmic lens. However, the incorporation of additives, in particular pigments, affects the properties of the anti-scratch coating.
Coatings which may be coloured after hardening are also known, using a dipping coloration method identical to that referred to for colouring the base substrates. The problems which arise are thus identical to those for the base substrates, because of the multiplicity of coatings, in particular anti-scratch coatings, used in the ophthalmic optics field.
It would thus be desirable to have access to a method which is rapid, reproducible and applicable to any type of substrate, whatever the material it is composed of.
In addition, such a method should allow production of the whole range of coloration, from the lightest colour (colour A) to the darkest (colour C).
The object of the invention is thus to solve these problems.
According to the invention, these objectives are achieved by a new method for incorporating at least one additive into a thin film formed on a substrate and comprising the following steps
(a) forming an impregnatable thin film on at least one face of the substrate;
(b) depositing an impregnation composition comprising at least one additive incorporated in an appropriate diluent medium on said impregnatable thin film by spin coating;
(c) diffusing the impregnation composition within said thin film and;
(d) treating the substrate coated with the impregnated thin film to at least partially remove the diluent medium from it.
The method according to the invention is particularly intended for the production of ophthalmic lenses but may find other useful applications.
By xe2x80x9cimpregnatable thin filmxe2x80x9d according to the invention, should be understood a film with thickness generally less than 5 xcexcm and composed of a material which allows the penetration into itself, by diffusion, of the additive(s) contained in the impregnation composition.
The impregnatable thin film preferably has a thickness of 0.5 to 2 xcexcm, typically of the order of 1 xcexcm.
The impregnatable thin film according to the invention may be composed of any material able to incorporate within itself, by diffusion, the additive(s) to be incorporated.
The material of the impregnatable thin films according to the invention is preferably an optically transparent material.
The material of the impregnatable thin film according to the invention is generally a polymeric material and preferably obtained from a latex.
As is well known, the latexes are dispersions of polymers in an aqueous phase.
Any type of latex, such as the poly(meth)acrylic latexes, the poly(meth)acrylic-styrene latexes and the polyurethane latexes may be used in the method of the invention.
The preferred latexes are the polyurethane latexes such as those disclosed in the European patent EP-0.680.492.
The impregnatable thin film according to the invention may be formed by any conventional known method. The formation of the impregnatable thin film may in particular be achieved by depositing a solution and/or dispersion of the impregnatable material on one or more faces of the substrate and drying this solution and/or dispersion to form the impregnatable thin film.
The deposit of the solution and/or dispersion of the impregnatable material may for example be achieved by dipping the substrate in the solution and/or dispersion, or, preferably, by depositing a solution and/or dispersion by spin coating.
The drying to obtain the thin film according to the invention may be carried out at ambient temperature or by heating, for example infrared heating or in an oven.
The substrate may be any substrate to which a thin film according to the invention will adhere. The substrate may in particular be an optically transparent material such as an organic or inorganic glass.
By substrate, in the sense of the present invention, should be understood an uncoated substrate or an already coated substrate, such as an ophthalmic lens optionally already coated. The thin film according to the invention is preferably applied to an uncoated substrate.
The impregnation composition according to the invention is a composition which contains at least one additive to be incorporated in an appropriate diluent medium.
The additives which may be incorporated include the dyes, the pigments, the plastifiers, the UV absorbers and the photochromic compounds. The preferred additives are dyes, pigments, and photochromic compounds.
The impregnation composition may be a solution and/or a dispersion of the additive to be incorporated.
The diluent medium is preferably a solvent, at least a partial solvent, of the additive(s) to be incorporated. More preferably, the diluent medium is a solvent of the additive(s) to be incorporated and the impregnation composition is a solution.
The solvent of the impregnation composition is optionally a solvent for swelling the material of the thin film, so as to facilitate the diffusion of the additive(s) within the thin film.
Also preferably, the impregnation composition is a solution and/or a dispersion of one or more dye(s), pigment(s) or photochromic compound(s).
As stated above, the impregnation composition is deposited by spin coating on the impregnatable thin film, which gives a film of the impregnation composition of uniform thickness, and in particular in the case of coloration solutions, a homogeneous coloration of the impregnatable thin film.
The film of the impregnation composition is then absorbed by the impregnatable thin film.
After impregnation of the thin film by the impregnation composition, the substrate coated with the impregnated thin film is dried, for example by infrared heating or in an oven.
The impregnation composition preferably contains an agent for retaining the additive, in other words a compound which has the effect of preventing the retrodiffusion of the additive towards the surface, in particular towards other films which might optionally be added to the impregnatable thin film, for example an anti-scratch coating in the case of an application to ophthalmic lenses.
In the case of an impregnatable thin film formed from a crosslinkable polymer, the retention agent is preferably a crosslinking agent or one which increases the crosslinking of the polymer.
Thus, in the case of an impregnatable thin film of polyurethane latex, the impregnation composition could contain a crosslinking agent which is an epoxyalkoxysilane hydrolysate, preferably an epoxytrialkoxysilane hydrolysate, and in particular xcex3-glycidoxypropyltrimethoxysilane (GLYMO). These epoxyalkoxysilane hydrolysates are known in the art and are disclosed among others in the patent FR 2.702.486.
The concentration of crosslinking agent in the impregnation composition is generally less than 25% by weight, preferably less than 20%, and even better less than 10% by weight.
The impregnation composition, when it contains a crosslinking agent, may also contain a hardening agent. In the case of an impregnation composition containing an epoxyalkoxysilane hydrolysate as crosslinking agent, the hardening agent is preferably an aluminium chelate, and especially aluminium acetylacetonate.
The use of a crosslinking agent and optionally a hardening agent in the impregnation compositions, when the thin film is a crosslinkable polymer, has the advantage of making the thin film resistant to solvent attack and preventing the retrodiffusion of the additive towards the surface.
This is important, particularly when a subsequent coating such as an anti-scratch coating is added. The composition for an anti-scratch coating generally contains an organic solvent when can, during the deposition, diffuse into the thin film and extract the additive if the thin film, for example a latex, does not contain a crosslinking agent.
Within the scope of the present invention, any anti-scratch coating conventionally used, in particular in the ophthalmic optics field, may be used. The preferred anti-scratch coatings are the anti-scratch coatings based on silane hydrolysates, in particular the epoxysilane hydrolysate such as that disclosed in the French patent FR 2.702.486 and the patent U.S. Pat. No. 4,211,823.
Obviously, it is also possible for other coatings conventionally used in the ophthalmic optics field, such as shock-proof and anti-reflection coatings, to be deposited onto the thin film according to the invention.
Other attractive aspects of the invention will be evident in the following description of an embodiment of the invention, described by way of a single non-limiting example, which refers to the annexed figures which schematically illustrate the principal steps of the method.